1. Technical Field
The present invention relates to bicycle parts, and more particularly, to a ratchet hub using a magnetic force to restore its unidirectional ratchet mechanism. The ratchet hub is advantageous for having less resistance and being free from problems related to elastic fatigue. Furthermore, the disclosed ratchet hub can be promptly switched between forward rotation for transmission and reverse rotation for restoration, without the risk of being jammed.
2. Description of Related Art
Conventionally, a rear hub of a bicycle implements a spring as a power source for restoring its unidirectional ratchet device. While the prior art uses a return spring that provides resilience large enough to restore the ratchet block, it suffers relatively large operational resistance. In addition, after long-term use, the spring tends to exhibit elastic fatigue that retards the unidirectional ratchet device from rapidly resorting to drive the hub.
On the other hand, Taiwan Patent No. M330208 has disclosed a hub ratchet device that includes a sleeve, a ratchet block, a ratchet ring being next to a freewheel device and more than one permanent magnets deposited on the ratchet block at an end distant from the freewheel device. The prior-art device employs the magnetic attraction generated among the permanent magnet, the ratchet block and the sleeve to restore the ratchet block, so that the ratchet ring and the freewheel device provide unidirectional transmission with reduced resistance and without the problem of elastic fatigue.
The prior-art device thus must have its ratchet block and sleeve made of magnetically permeable metal. Moreover, the ratchet block has to be such processed that one end thereof is formed with annularly arranged teeth for engaging the sleeve and that its surface interfacing sleeve limits rotation of the sleeve. In the event that the ratchet block and the sleeve are directly made by processing magnetically permeable metal, their magnetism is likely to reduce or lose due to cutting, high heat and/or impact during their processing. In the event that the ratchet block and the sleeve are first shaped and then magnetized, additional processing procedures are required and therefore the manufacturing cost is increased. Besides, since the shaped ratchet block and the sleeve are uneven in surface, the magnetization may be ineffective.
Moreover, because most components of the prior-art device, particularly the freewheel device, are made of magnetically permeable metal, when the ratchet block has its annularly arranged teeth engaging with the freewheel device, the magnetism of the ratchet block further strengthen the combination, and causes the ratchet block to be inseparable from the freewheel device, thereby hindering the reverse rotation of the ratchet device. The magnetism of the ratchet block also tends to attract foreign iron dust that causes addition wear to the components of the device.